1. Field of the Invention
The present invention relates generally to pumps and, more specifically, to a system and method for preventing floating rod effect in a reciprocating pump having a pump rod.
2. Description of the Related Art
This section is intended to introduce the reader to aspects of art that may be related to aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
A pump typically is used to lift oil from a subterranean oil reservoir to the surface. There are many different types of pumps that have been used to pump oil from an oil well. A commonly used type of pump for retrieving oil from a wellbore is known as a “sucker rod” pump unit. A sucker rod pump unit is a system that operates a downhole reciprocating pump linked to a surface prime mover by a rod string. The pump produces well fluids to the surface through production tubing. The rod string runs inside the production tubing and is connected to a piston within the downhole pump. The rod string is immersed in the well fluids. The opposite end of the sucker rod is supported by a bridle coupled to a reciprocating unit. The reciprocating unit lifts the bridle and the sucker rod string to produce an upward stroke of the downhole reciprocating pump. The downward stroke of the downhole reciprocating pump is achieved by letting gravity pull the rod string downward. The downhole pump may include a piston having a check valve. As the sucker rod string is lifted upward, the check valve is closed, and oil and other wellbore fluids are lifted by the plunger upward towards the surface. As the sucker rod falls downward, the check valve opens and oil and other well fluids are allowed to flow into the pump above the piston.
Because the rod string is immersed in the well fluids in the production tubing, the ability of the sucker rod to fall through the well fluids is effected by the viscosity of the well fluids. When the bridle that supports the sucker rod descends faster than the sucker rod string, the bridle may separate from the sucker rod string. When the reciprocating unit begins lifting the bridle, the sucker rod may still be descending. This can cause a violent impact when the bridle engages the sucker rod, leading to failure of the sucker rod or the bridle. It also means that the pumping unit is not producing oil during a full upward stroke. This condition is known as “floating rod effect”.
The techniques described below address one or more of the problems associated with “floating rod effect”.